According to a recent study published in the journal Environmental Health Perspectives, in which nearly 300 sets of mothers and children in Mexico were evaluated, and the children tested twice for cognitive development over the course of 12 years, it was found that increased levels of prenatal fluoride exposure may be associated with lower cognitive function in children.

While fluoride is not added to the drinking water in Mexico, individuals are exposed to it through naturally occurring fluoride in water and fluoridated salt and supplements.

According to the study, there was a drop in scores on intelligence tests for every 0.5 milligram-per-litre increase in fluoride exposure beyond 0.8 milligrams per litre found in urine. While researchers found a potential connection to a child’s exposure to fluoride in utero, they found no significant influence from fluoride exposure on brain development once a child was born.

The study’s lead author, Howard Hu, founding dean of the Dalla Lana School of Public Health at the University of Toronto, said: “Childhood exposure to fluoride is safer than prenatal. There is pretty good science now to support the fact that the foetal system tends to be more sensitive to environmental toxicants than once the child is born.”

The authors measured fluoride exposure for the Mexican mothers and their children by looking at the chemical content in their urine as opposed to previous studies which measured fluoride exposure by analysing it in the environment, such as in water.

Previous studies have found fluoride to be a potential neurotoxin at extremely high levels. Many of these studies have been conducted in China, where fluoride levels in water can be as high as 30 milligrams per litre.

Scientists agree that extreme fluoride levels, like those sometimes found in China, can have neurodevelopmental risks. But as the study also points out, fluoridation also “substantially reduces the prevalence and incidence of dental caries.”

If you are concerned about the amount of fluoride you or your family are ingesting, especially as fluoride has also been linked to cancer, the best way to ensure that your drinking water is free of this toxin is to invest in a water cooler with a good filter.